Retention assembly with  a conical interface for a propeller blade

ABSTRACT

A retention assembly for a propeller blade includes an inner ring that is conformally shaped to a bore of an annular loop, the annular loop being associated with a root portion of the propeller blade; a base that is configured to be immediately adjacent the annular loop; an annular outer ring including a bearing race interface that is conical in shape and includes a radially inner surface that conforms to a radially outer surface of the annular loop; and an adhesive that adhesively connects complementary surfaces of the outer ring and the annular loop. Also, a propeller blade assembly includes a propeller blade having a blade portion and a root portion; and the retention assembly that is configured to attach to the propeller blade.

BACKGROUND

The subject matter disclosed herein relates generally to propellersystems and blades and, more particularly, to a lightweight propellerblade assembly with a conical blade to sleeve interface.

DESCRIPTION OF RELATED ART

Modern propeller blades typically incorporate composite materials thatreduce weight and enhance performance. The composite blades typicallyinclude a blade portion and a root portion which extends into a hub armof the hub of a propeller system and which is secured to and rotatablerelative to the hub arm via a retention assembly. A challenge withlightweight composite blades is that a bending moment (BM) capacity ofthe retention assembly to the hub arm is often reduced due to a lowercentrifugal load (CL) of the blade. A typical lightweight propellerblade using a type of arrangement to address BM includes the systemshown in U.S. Pat. No. 6,676,080. As can be seen from the drawings ofthis patent, the bearing races are sized for bearings that can withstandbending moments, but the interface between the composite blade and outerring bearing race may become unloaded due to insufficient centrifugalloading. This is an undesirable condition which may reduce the life ofthe composite blade portion and/or outer ring.

Thus, there is a need for a lightweight propeller blade with a conicalblade to sleeve interface that can withstand high bending moments atlower centrifugal loading.

BRIEF SUMMARY

According to an aspect of the invention, a retention assembly for apropeller blade includes an inner ring that is conformally shaped to abore of an annular loop, the annular loop being associated with a rootportion of the propeller blade; a base that is configured to beimmediately adjacent the annular loop; an annular outer ring including abearing race interface that is conical in shape and includes a radiallyinner surface that conforms to a radially outer surface of the annularloop; and an adhesive that adhesively connects complementary surfaces ofthe outer ring and the annular loop.

According to another aspect of the invention, a propeller blade assemblyincludes a propeller blade including a blade portion and a root portion;and a retention assembly configured to attach to the propeller blade.The retention assembly includes an inner ring that is conformally shapedto a bore of an annular loop, the annular loop being associated with aroot portion of the propeller blade; a base that is configured to beimmediately adjacent the annular loop; an annular outer ring including abearing race interface that is conical in shape and includes a radiallyinner surface that conforms to a radially outer surface of the annularloop; and an adhesive that adhesively connects complementary surfaces ofthe outer ring and the annular loop.

Other aspects, features, and techniques of the invention will becomemore apparent from the following description taken in conjunction withthe drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The subject matter, which is regarded as the invention, is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which like elements arenumbered alike in the several FIGURES:

FIG. 1 is a plan view of an aircraft according to an embodiment of theinvention; and

FIG. 2 is a cross-sectional view of a propeller blade assembly of FIG. 1according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings, FIG. 1 is a plan view of an aircraft 10having a plurality of lightweight propeller blade assemblies 22 with animproved retention assembly 32 according to an embodiment of theinvention. The aircraft 10 includes a fuselage 12, a cockpit 14, and atail 16. Attached to the fuselage 12 are left and right wings 18 a, 18 brespectively. Each wing 18 a, 18 b incorporates a respective propeller20 a, 20 b that is aligned on respective axes A, B. Each propeller 20 a,20 b includes a plurality of propeller blade assemblies 22 that aredriven for rotation by respective gas turbine engines 24 a, 24 b.Although a specific aircraft is illustrated and described herein, otherpropeller driven aircrafts are within the scope of the invention.

Referring to FIG. 2, a cross-section view of a lightweight propellerblade assembly 22 that includes a conical blade to sleeve interface isillustrated according to an embodiment of the invention. The propellerblade assembly 22 includes a propeller blade 30 that is received andsecured to a retention assembly 32. The propeller blade 30 includes ablade portion 34 that terminates into a root portion 36. The propellerblade 30 is generally cylindrical in shape at root portion 36 andtransitions to an airfoil shape that thins and flattens toward a tip(not shown) which is directionally opposite root portion 36 in adirection of arrow 39 (i.e., from inboard/hub end to an outboard/tip endof the propeller blade 30). In embodiments, a shape of propeller blade30 may also spiral or twist toward the tip (not shown) in a known manneraccording to the type of propeller blade that is used. In embodiments,propeller blade 30 including blade portion 34 and root portion 36 may beconstructed of one or more layers of unidirectional and/or woven glassfibers, and one or more layers of unidirectional and/or woven graphitefibers that are embedded in a suitable resin material as is well-knownto a person of ordinary skill in the art. The root portion 36 isconfigured to attach to a retention assembly 32. The root portion 36includes an annular loop 38 that forms a teardrop-shaped bore 41. It isto be appreciated that the retention assembly 32 is configured to attachto the propeller blade 30 and increase a bending moment capacity of thepropeller blade retention for lower centrifugal loads, as will bedescribed in greater detail below.

Retention assembly 32 includes an inner ring 40, an outer ring 42, base44, and a sleeve 46. In embodiments, rings 40, 42 may be machined fromhigh strength stainless steel, although aluminum, titanium or othersuitable metals or composites may be used. Inner ring 40 is an annularring and may be conformally shaped to bore 41 (i.e., inner ring 40 has atear-drop shaped cross-section) and is located inside theteardrop-shaped bore 41. The base 44 is annular and is positionedimmediately adjacent annular loop 38 and includes a lower end 48 thatinterfaces with a bottom surface of annular loop 38, a wall 50 thatinterfaces with an inner surface 56 of annular loop 38, and a lateralportion 52 that generally resides within a hollow root cavity 54. Thewall 50 extends upwardly (in direction of arrow 39) from lower end 48into a hollow root cavity 54 and is in frictional engagement with innersurface 56 of root portion 36. A balance tube 88 extends through acentral opening defined by lateral portion 52 in base 44. The balancetube 88 and lateral portion 52 close hollow root cavity 54 of rootportion 36 to prevent intrusion of oil and/or moisture into the hollowroot cavity 54 which may otherwise damage propeller blade 30. Theannular loop 38 and inner ring 40 are sandwiched between base 44 andouter ring 42. The base 44 may be machined from aluminum material, butmay alternatively be constructed of other materials, such as steel,composites, or the like.

The outer ring 42 is generally annular in shape and includes, movingfrom an inboard/hub end to an outboard/blade tip end, a bearing raceinterface 58, a bearing race groove 60, a plurality of flanges 62, 64that define a lower annular groove 66, and an upper annular groove 68that terminates into an annular flange 70. The bearing race interface 58is generally conical in shape and includes a radially inner surface 72that is complementary to a radially outer surface 74 of annular loop 38.The annular loop 38 and outer ring 42 are adhesively bonded to eachother at these surfaces 72, 74 in order to subject the interface, formedby connecting surfaces 72, 74, primarily to shear stresses rather thanpeel stresses which is not the case in prior art propeller blades whichprimarily sees peel stresses when subjected to high bending momentsrelative to the centrifugal loading. In the present invention,increasing the overall shear stresses at this interface increases abending moment capacity of the propeller blade retention assembly 32. Inembodiments, the adhesive could be a structural adhesive such as anepoxy and/or a compliant epoxy such as polyurethane, polysulfide or RTVsilicone. In one example, Hysol® EA 9346.5 epoxy paste adhesivemanufactured by the Henkel Corporation may be used as the structuraladhesive.

Also illustrated in FIG. 2, bearing race groove 60 is a bearing racethat receives a bearing assembly 76 such as, for example, an angularcontact ball bearing assembly, tapered roller bearing assembly, deepgroove thrust or roller bearing assembly, two-piece bearing raceassembly, or the like. Although a single bearing race groove 60 is shownand described, in an embodiment, two or more bearing race groovessubstantially similar may also be provided for use with a propeller hubthat can use a multi-row bearing assembly. Flanges 62, 64 define anannular groove that is adapted to receive an annular O-ring 66. Theflanges 62, 64 bear against a retaining surface 80 of a propeller hub 78to contain the O-ring 66. The bearing race groove 60 cooperates with thehub race groove 61 to contain the bearing assembly 76 and preventseparation of propeller blade assembly 22 from propeller hub 78 whenhigh outward centrifugal force is applied in a direction of arrow 82during rotation of propeller hub 78. Upper annular groove 68 is adaptedto receive a locking ring (not shown) for holding propeller bladeassembly 22 against movement into the propeller hub 78 when not in use.Also, upper annular groove 68 terminates into an annular flange 70.

A sleeve 46 extends between outer ring 42 and root portion 36. Sleeve 46may be adhesively bonded to outer ring 36 and to root portion 42 and isa single-piece construction and may be molded of a plastic material,such as Delrin® manufactured by Dupont™ or other acetal material,polyurethane, etc. The sleeve 46 has an annular flange 84 that abutsagainst annular flange 70 of outer ring 42 and a wedge-shaped portion 86that extends downwardly from annular flange 84 (i.e., toward propellerhub 78) between outer ring 42 and root portion 36. Sleeve 46 acts as alower modulus cushion, which can be approximately 50 times less stiffthan steel, for absorbing bending loads from blade portion 34. Inembodiments, the adhesive could be a structural adhesive such as anepoxy and/or a compliant epoxy such as polyurethane, polysulfide or RTVsilicone.

In prior art propeller blades, the retention capacity of an interfacebetween the composite blade and outer ring bearing race may becomeunloaded due to insufficient centrifugal loading which may reduce thelife of the blade portion and/or the outer ring of the propeller blade.However, benefits of the present invention with a use of a conicalshaped bearing race interface 58 that is adhesively coupled to rootportion 36 along mutual interfaces provides an improved retentioncapacity propeller blade assembly 22 because it increases a bendingmoment capacity of the propeller blade 30. Additional benefits of usingan adhesive is that an adhesive layer between the contact surface ofouter ring 42 and a root portion 36 of propeller blade 30 providesprimarily shear stresses in the propeller blade 30 and minimizes peelstresses thereby preventing unloading of the propeller blade 30 at thebearing race interface 58.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention.While the description of the present invention has been presented forpurposes of illustration and description, it is not intended to beexhaustive or limited to the invention in the form disclosed. Forinstance, aspects of the invention are not limited to propeller bladesfor aircraft, and can be used in wind turbines and other systems withrotary elements. Many modifications, variations, alterations,substitutions, or equivalent arrangement not hereto described will beapparent to those of ordinary skill in the art without departing fromthe scope and spirit of the invention. Additionally, while the variousembodiment of the invention have been described, it is to be understoodthat aspects of the invention may include only some of the describedembodiments. Accordingly, the invention is not to be seen as limited bythe foregoing description, but is only limited by the scope of theappended claims.

What is claimed is:
 1. A retention assembly for a propeller blade,comprising: an inner ring that is conformally shaped to a bore of anannular loop, the annular loop being associated with a root portion ofthe propeller blade; a base that is configured to be immediatelyadjacent the annular loop; an annular outer ring including a bearingrace interface that is conical in shape and includes a radially innersurface that conforms to a radially outer surface of the annular loop;and an adhesive that adhesively connects complementary surfaces of theouter ring and the annular loop.
 2. The retention assembly of claim 1,wherein the outer ring further comprises a bearing race groove, a lowerannular groove, and an upper annular groove.
 3. The retention assemblyof claim 2, further comprising a bearing assembly coupled to the bearingrace groove.
 4. The retention assembly of claim 2, wherein the outerring further comprises a plurality of annular flanges that contains thelower annular groove.
 5. The retention assembly of claim 2, wherein thelower annular groove is configured to receive an annular O-ring.
 6. Theretention assembly of claim 1, further comprising a sleeve that isadhesively connected to each of the root portion and the outer ring. 7.The retention assembly of claim 1, wherein the adhesive couples theradially inner surface of the bearing race interface to the radiallyouter surface of the annular loop.
 8. The retention assembly of claim 1,wherein the annular loop is configured to receive the inner ring withinthe bore.
 9. A propeller blade assembly, comprising: a propeller bladeincluding a blade portion and a root portion; and a retention assemblyconfigured to attach to the propeller blade, the retention assemblyfurther comprising: an inner ring that is conformally shaped to a boreof an annular loop, the annular loop being associated with a rootportion of the propeller blade; a base that is configured to beimmediately adjacent the annular loop; an annular outer ring including abearing race interface that is conical in shape and includes a radiallyinner surface that conforms to a radially outer surface of the annularloop; and an adhesive that adhesively connects complementary surfaces ofthe outer ring and the annular loop.
 10. The propeller blade assembly ofclaim 9, wherein the outer ring further comprises a bearing race groove,a lower annular groove, and an upper annular groove.
 11. The propellerblade assembly of claim 10, further comprising a bearing assemblycoupled to the bearing race groove.
 12. The propeller blade assembly ofclaim 10, wherein the outer ring further comprises a plurality ofannular flanges that contains the lower annular groove.
 13. Thepropeller blade assembly of claim 10, wherein the lower annular grooveis configured to receive an annular O-ring.
 14. The propeller bladeassembly of claim 10, further comprising a hub having a hub race groovethat is coupled to the bearing assembly.
 15. The propeller bladeassembly of claim 9, further comprising a sleeve that is adhesivelyconnected to each of the root portion and the outer ring.